Production of fuel gas

ABSTRACT

Fuel gas suitable for use in conjunction with a gas turbine is prepared by subjecting a hydrocarbon oil to partial combustion using air as the oxidizing medium and injecting additional hydrocarbon oil into the hot partial combustion products.

United States Patent [191 Slater et al. 1

PRODUCTION OF FUEL GAS Inventors: William L. Slater, La Habra;

Warren G. Schlinger, Pasadena; William B. Crouch, Whittier, all of Calif.

Assignee: Texaco Inc., New York, NY.

Filed: Nov. 4, 1971 Appl. No.: 195,771

[ Jan. 8, 1974 [56] References Cited UNITED STATES PATENTS 2,692,193 10/1954 Riesz et al. 48/214 3,201,215 8/1965 Negra et al. 48/215 Primary Examiner-Joseph Scovronek Attorney-Thomas H. Whaley et al.

[57] ABSTRACT Fuel gas suitable for use in conjunction with a gas tur- U-S. i. R, bine is prepared subjecting a hydr carbon to 48/214 partial combustion using air as the oxidizing medium Inl. l u; l and injecting additional hydrocarbon into the hot 01 Search R, 3, partial combustion products 13 Claims, 1 Drawing Figure r55 sew/9am F052 145 AIR/16475,?- 2 Z0 1 5 Z/ 20 22 Z4 Z5 Z] F//?sr saw/v0 i 1 fin/mama GENERATOR OIL HEATER PRODUCTION or FUEL GAS This invention relates to the production of fuel gas. More particularly it relates to the production of fuel gas by the partial oxidation of hydrocarbon liquids. In one of its more specific aspects it is concerned with the production of a fuel gas, for use in turbines, using air as the oxidizing agent for the partial combustion.

It is known to produce gaseous fuels by the partial oxidation of hydrocarbon liquids. The prior art suggests air, oxygen-enriched air or relatively pure oxygen as the oxidizing agent. However, so far as is known, only processes in which oxygen-enriched air or relatively pure oxygen is used as the oxidizing agent have attained any commercial significance. It is possible, as the art suggests, to carry out a partial oxidation process using air as the oxidizing agent but unfortunately such processes have not been satisfactory for the production of fuel gases because, due to the high nitrogen content of the air, the product gas has an undesirably high content of inert material and a correspondingly low BTU value. Accordingly, to produce a gas of low nitrogen content and high BTU value, commercial processes ordinarily use either oxygen or oxygen-enriched air as the oxidizing medium.

It is possible to improve the BTU value of a partial oxidation product gas or synthesis gas by the addition of methane thereto but this is not economical because of the shortage of natural gas. Carrying out the partial oxidation at a temperature of about l,300 to 1,600 F. to increase the methane content has also been suggested. However, operation at this temperature level is not advisable as there is the danger of a flame-out and a resulting explosion. There is therefore need for a satisfactory process for the production of gaseous fuel from hydrocarbon liquids by partial oxidation using air or a gas containing about 19-21 percent oxygen as the oxidizing agent.

According to our invention, there is provided a process for the production of fuel gas which comprises subjecting a hydrocarbon liquid optionally in the presence of steam to partialcombustion with a gas having a low oxygen content such as air at a pressure between about 30 and 3,000 psig and at an autogenouslymaintained temperature between about 1,600 and 3,000 F to produce a product gas comprising principally nitrogen, carbon monoxide and hydrogen, injecting hydrocarbon liquid and steam into the product gas stream at substantially the pressure of the partial oxidation zone to cool the product gas and heat the steamyydrocarbon mixture to a temperature below 1,800 F. and above l,000 F to convert at least a portion of said injected hydrocarbon liquid to methane, cooling the resulting product to condense water therefrom and recovering a product gas composed principally of carbon monoxide, nitrogen, hydrogen and methane.

The hydrocarbon liquid used as feed to the process of this invention may be any refinery stream such as naphtha, kerosene, gas oils or residue-containing oils such as whole crude, atmospheric residua, tar sand oil, shale oil or their mixtures and the like. In this connection it should be understood that the terms hydrocarbon oil and hydrocarbon liquid are used interchangeably and include oils ,or liquids containing minor amounts of impurities, such as sulfur, nitrogen and metals. The oil feed is preheated to a temperature of be tween about 200 and 900 F. preferably 250 to 800 F. and if desired mixed with steam. lf the oil is liquid at preheating temperature, it is preferably injected as a steam-oil suspension into a gas generator maintained autogenously at a temperature between about 1,600 and 3,000 F preferably between about 2,000 and 2,500 F. To prevent the possibility of a flame-out, the temperature should be kept above 1,600 F. The hydrocarbon to steam ratio is between about 10 to l and l to 5 preferably about 5 to l by weight. To support the partial oxidation reaction, air preferably preheated to between 500 and l,800 F. is introduced into the gas generation zone at an oil to air weight ratio of about 0.15 to 0.20 preferably 0.18. Pressure in the gas generation zone is maintained at between about 30 and 3,000 psig or higher preferably between 200 and 500 psig. Product gas composed principally of carbon monoxide, hydrogen, nitrogen and carbon dioxide leaves the generator at approximately reaction temperature.

After leaving the first gas generation zone the partial oxidation product is mixed with additional hydrocarbon oil and steam. The hydrocarbon oil injected into the product stream may be the same type of oil used as feed stock to the first gas generation zone although it is not necessarily limited thereto. Preferably the injected oil is a distillate oil and more preferably it boils in the naphtha range. A particularly suitable oil for injection at this point of the process is a substantially paraffinic naphtha obtained as a raffinate from a process in which the aromatic hydrocarbons have been removed. In another embodiment, a hydrocarbon oil can be fractionated into alight fraction and a heavy fraction, the light fraction being used as feed to the first gas generator and the heavy fraction as a scrubbingmedium for the removal of entrained particles of carbon from the product gas. The resulting heavy oil-carbon slurry may then be fed to the first generatonThe light fraction may also be injected into the gaseous products leaving the first gas generation zone. lt is also possible to use the light fraction as the oil injected into the sec-- tion conditions then the oil and steam are injected as a vaporous mixture. If the oil is liquid at injection conditions then preferably it in injected into the partial oxidation product gas stream as an oil steam suspension.

7 The mixing may take place in the second gas genera tion zone or upstream thereof.

The oil and steam are injected into the product gas in a ratio of 0.5 to l to 10 to 1 parts of oil per part of steam by weight. The reaction conditions in the second gas generation zoneare such that no water is present as liquid. The residence time of the reactants in the second generation zone will vary according to the type of oil injected and the pressure and temperature within the reaction zone. Residence times of from onc-half second to 2 minutes may be used although residence times of from 1 second to 10 seconds ordinarily will result in substantial conversion of most injected oils to methane.

After the injected oil is in part converted to methane in the second gas generation zone the product gases are subjected to cooling to recover heat therefrom. Advantageously this is accomplished by passing the product gases through a waste heat boiler or a heat exchanger for the production of steam or in another embodiment for the preheating of the oil charge stock to the first gas generation zone product gas for conversion to methane in the second gas generation zone. In either event conditions within the waste heat boiler or heat exchanger should be such that no condensation of steam to form liquid water takes place.

The partially cooled gases leaving the waste heat boiler or heat exchanger then pass to a scrubbing zone. The scrubbing or clean-up of the product fuel gas may comprise several steps. For example, the product gas from the heat exchanger may be subjected to scrubbing with water or hydrocarbon oil for the removal of any traces of carbon present therein.

For the removal of H 5 and CO from the product gas, various solvents such as ethanolamine, N-methylpyrrolidone or methanol may be used. Methanol is preferred because of its special properties that make it possible to separate the removed H S and CO for ultimate disposal.

Advantageously, all of the steps described above take place at substantially the pressure of the first gas generation zone taking only the necessary pressure drop to permit the reactants to flow through the system.

Not only is the product gas satisfactory for use as a fuel, it is particularly satisfactory for use as a fuel in connection with the operation of gas turbines. A distinct advantage of the product fuel is that its combustion products are substantially free from pollutants and may be exhausted directly to the atmosphere. Another advantage of the process of our invention is its high thermal efficiency. 1f the charge stock to the process of our invention is used as a fuel for the production of steam to operate a turbine, the efficiency of conversion of thermal energy to mechanical energy is approximately 34 percent whereas if our process is followed and the combustion products of our product fuel are used to operate a gas turbine and the steam produced in cooling the combustion gases is used to drive additional turbines, the efficiency is increased to nearly 50 percent.

An example of the invention will now be given in conjunction with a description of the accompanying drawing which represents a flow diagram for the practice of one embodiment of the invention. The charge, an atmospheric residium, has an initial boiling point of 650 F. and a sulfur content of 2.0 wt. percent.

lnto first generator 11 an unpacked, lined reactor having an internal volume of cubic feet, air is introduced through line 12, heater 13 and line 14, steam through line 15 and charge oil through line 16, heater 17 and line 18. Air temperature in line 14 is l,200 F., oil temperature in line 18 is 250 F. and steam temperature in line 15 is 650 F. The oil is introduced at a rate of 550 lbs/hr. with the oil: air weight ratio being 0.15 and the oilzsteam weight ratio 6.67. Pressure in first generator 11 is 200 psig and the temperature is maintained autogenously at 2,350 F. Additional charge oil at a temperature of 400 F. is introduced through line 20 and mixed with an equal weight of 800 F. steam in line 21 and the mixture introduced into line 22 to mix with the partial oxidation product gases leaving first generator 11. Although in the drawing it is shown that the oil and. steam are introduced into transfer line 22 for mixture with the product gas leaving first generator 11, it is also possible to introduce the oil and steam directly into second generator 23. As result of injecting oil and steam into the hot product gas exiting first generator 11 the temperature of the resulting mixture as it enters second generat0r23 is 1,700 "F. Residence time in the second generator is 3 seconds. On leaving second generator 23 the product fuel gas is passed through line 24 and waste heat boiler 25 for the generation of steam and then passes through line 26 into scrubber 30, which represents two scrubbing zones, an initial oil scrubbing zone where the product gas is scrubbed with oil from line 32 for the removal of solid particles such as carbon entrained in the gas and also to effect additional cooling, and a second zone where the scrubbed gases are contacted with methanol from line 33 and cooled to a temperature of 55 F. at a pressure of psig for the removal of CO and H S. The product fuel gas leaving scrubber 30 contains 18.2 percent CO, 14.6 percent Hi, 12.9 percent CH 53.6 percent N and 0.7 percent A and has a heating value of 234 BTU per cubic foot. It is suitable for use in gas turbines and its combustion products may be exhausted directly to the atmosphere. Carbon-oil slurry is removed from scrubber 30 through line 34 and in a commercial installation would be sent to the first gas generator for partial combustion therein.

The heating value of the product fuel may be varied by adjusting the amount of hydrocarbon liquid introduced into the second gas generation zone and the temperature, pressure and residence time therein. In this way, fuel gases having a heating value of more than 150 BTU/cu. ft. and up to 1,000 BTU/cu. ft. can be made using air as the oxidizing medium for the partial combustion step.

It is also possible to scrub carbon from the gas with water and then contact the water with oil to remove the carbon therefrom to form a carbon-oil composite which may be used as feed to the first gas generation zone.

Obviously, many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof and therefore only such limitations should be made as are indicated in the appended claims.

We claim:

1. A process for the production of fuel gas which comprises subjecting a petroleum hydrocarbon liquid in the presence of steam to partial combustion in an unpacked first gas generation zone with a gas comprising air at a pressure between about 30 and 3,000 psig and at an autogenously-maintained temperature between about 1,600 and 3,000 F. using a hydrocarbon to steam weight ratio between 10:1 and 1:5 and a hydrocarbon to air weight ratio between 0.15 and 0.2 to produce an effluent gas comprising nitrogen, carbon monoxide and hydrogen, injecting hydrocarbon liquid and steam into the effluent gas stream at substantially the pressure of the partial combustion zone to cool the effluent gas and heat the steam-hydrocarbon mixture to a temperature below about 1,800 F. and above 1,000 F to convert at least a portion of said injected hydrocarbon liquid to methane in a second gas generation zone, cooling the resulting product to condense water therefrom and recovering a product gas composed principally of carbon monoxide, nitrogen, hydrogen and methane and having a heating value between 150 and 1,000 BTU/cu. ft.

2. The process of claim 1 in which the pressure in the partial combustion zone is between 200 and 500 psig.

3. The process of claim 1 in which the hydrocarbon liquid boils in the naphtha range.

4. The process of claim 1 in which the temperature in the partial combustion zone is between 2,000 and 2,500 F.

5. The process of claim 1 in which the cooled product is contacted with N-methyl-pyrrolidone.

6. The process of claim 1 in which the cooled product is contacted with ethanolamine.

7. The process of claim 1 in which the cooled product is contacted with methanol.

8. The process of claim 1 in which the hydrocarbon to air ratio is 0.15 and the hydrocarbon to steam ratio is 6.67.

9. The process of claim 1 in which the first gas generation zone, the second gas generation zone and the cooling zone are maintained at substantially the same pressure.

10. The process of claim 1 in which a hydrocarbon oil is fractionated into a light fraction and a heavy fraction and the heavy fraction is used as a scrubbing medium to remove entrained solid particles from the gaseous product of the second gas generation zone.

11. The process of claim 10 in which the light fraction is introduced as feed to the first gas generation zone.

12. The process of claim 10 in which the light fraction is injected into the effluent gas stream.

13. The process of claim 10 in which the heavy fraction-carbon mixture is introduced as feed to the first gas generation zone. 

2. The process of claim 1 in which the pressure in the partial combustion zone is between 200 and 500 psig.
 3. The process of claim 1 in which the hydrocarbon liquid boils in the naphtha range.
 4. The process of claim 1 in which the temperature in the partial combustion zone is between 2,000* and 2,500* F.
 5. The process of claim 1 in which the cooled product is contacted with N-methYl-pyrrolidone.
 6. The process of claim 1 in which the cooled product is contacted with ethanolamine.
 7. The process of claim 1 in which the cooled product is contacted with methanol.
 8. The process of claim 1 in which the hydrocarbon to air ratio is 0.15 and the hydrocarbon to steam ratio is 6.67.
 9. The process of claim 1 in which the first gas generation zone, the second gas generation zone and the cooling zone are maintained at substantially the same pressure.
 10. The process of claim 1 in which a hydrocarbon oil is fractionated into a light fraction and a heavy fraction and the heavy fraction is used as a scrubbing medium to remove entrained solid particles from the gaseous product of the second gas generation zone.
 11. The process of claim 10 in which the light fraction is introduced as feed to the first gas generation zone.
 12. The process of claim 10 in which the light fraction is injected into the effluent gas stream.
 13. The process of claim 10 in which the heavy fraction-carbon mixture is introduced as feed to the first gas generation zone. 